Wireless communications networks following the protocols of the standard known as IEEE 802.16 may use various types of message tracking and may use multiple levels of acknowledgement in order to promote high traffic throughput and reliable communications in the networks. Hybrid Automatic Repeat Request (HARQ) protocols may be used at the PHY level for fast response, while Automatic Repeat Request (ARQ) protocols may be used at the MAC level when the HARQ protocols don't provide sufficient reliability. For message tracking, each transmission may contain a HARQ Channel ID (ACID) to track the message and its acknowledgement. The available ACID's for use between a base station and a particular subscriber station are limited in number and must be repeatedly recycled. A single-bit parameter called a HARQ Sequence Number (AI_SN) may be associated with each ACID to indicate whether the current transmission is a new transmission or a retransmission of a previously NAK'd transmission. A retransmission will contain the same ACID and same AI_SN as the original transmission that was NAK'd. A new transmission is indicated when the AI_SN has the opposite value that it had the last time the current ACID was used.
To handle acknowledgements, errors in a received transmission are initially detected and handled at the PHY layer using HARQ. If the transmission is received correctly, the receiving device may transmit a PHY-level ACK back to the originating device, which then removes that transmission from its PHY-level buffers. But if the transmission is received incorrectly, a PHY-level NAK is transmitted back, still following the HARQ protocol, and the originating device retransmits the data. If the PHY-level retransmissions also fail a certain number of times, this failure is then passed to the MAC layer of the receiving device, which initiates a MAC-level NAK using the ARQ protocol, so that the originating device can take more drastic action. MAC-level exchanges of this type are much more time-consuming, which hurts the efficiency of communications between the two devices. Unfortunately, HARQ ACKs and NAKs may be expressed by a single bit that is not protected by CRC or other error detection techniques, so the originating device may erroneously receive a HARQ NAK as a HARQ ACK without knowing of the error. It would then clear the associated transmission from its PHY-level buffer, thus losing any chance to retransmit the data until the receiver's MAC layer notifies the originating device of the missing data. At that point, recovering from the error is much more difficult and time-consuming.